1. Requirement of the extension of hold-up time

The demand for the longer hold-up time is increasing in order to keep output voltage during the instantaneous interruption. Adding a smoothing capacitor enables to extend hold-up time (Th), and adding output capacitor enables to extend fall time(Tf).

2．Extension method of hold-up time

1) In the case of AC-DC converter

It is necessary to increase the capacitance of smoothing capacitor on primary side to extend hold-up time.
The TU series have design flexibility and hold-up time can be extended by adding a smoothing capacitor externally.
In LFP240F/300F, the external capacitor unit is available as optional parts (available only with -U1Y option).

2)In the case of DC-DC converter

It is necessary to add an external capacitor between +Vin and -Vin to extend hold-up time.

3．Calculation formula of required capacitance for hold-up time

External capacitor (Cbc) value can be calculated with following formula.

Calculation example
-Product: TUHS10F05
-Input voltage: 100Vac
-Output power: 4W
-Required hold-up time: 200ms
-Ambient temperature: -20ºC

1) Efficiency(η) and minimum input voltage for regulated output voltage(Vh) of TUHS10F05 are listed in test data.
    η：Efficiency (by Load Current) of P.4 at test data, at 100Vac, 0.8Aout, Efficiency is 80.6%.
    Vh：Minimum Input Voltage for Regulated Output Voltage of P.21 at test data, at 50%out, -20ºC,
        Minimum Input Voltage for Regulated Output Voltage is 38Vac.

2) Cbc value can be calculated by above formula.